The application of lamp string has been widely used, such as Christmas lamp string, landscape lamp string, and building lamp string, etc. As for the progress of process for the light emitting diode (LED) and lower price thereof, it becomes a new trend to apply LED in the lamp string. But, because LED is basically suitable for DC power and the lamp string is applied in the AC power environment, there have been some products in the market to apply LED in the lamp string. However, how to achieve the synchronous changing will be an obstacle to overcome. The present invention has studied this subject and obtained solid result, so as to submit the patent application.
The current LED lamp string employs the prior art shown in FIG. 1, FIG. 2 and FIG. 3; wherein, each light emitting module represents a set of RGB (three colors) LED lamp unit 2. In the prior art, the technique shown in FIG. 1 is the most undesirable, in which the lamp employed DC parallel type to make all LED lamp units 2 in parallel, so that it has large current consumption, i.e. the power adapter 1 is hard to handle, or with higher cost, or with limited number of LED lamp units 2 in parallel in order to supply large current.
The technique shown in FIG. 2 is better than the technique shown in FIG. 1. Because the LED lamp unit 2 is in serial connection, the current consumption is smaller; and, the power adapter 1 is easily handled and with lower cost. But, this technique still has a defect that the number of LED lamp units 2 to be serially connected are limited, which is determined by the DC voltage supplied by the power adapter 1, i.e. the higher DV voltage, the more LED lamp units 2 to be connected.
The technique shown in FIG. 3 is the best method among the three, which is to replace the power adapter 1 shown in FIG. 1 with each small power adapter 1; wherein, the structure of the small power adapter 1 is simpler, and the lamp units 2 able to be connected have no limits. The only defect is that one LED lamp unit 2 must be associated with one small power adapter 1, so that the product cost is higher.
In the prior art shown in FIG. 1, FIG. 2 and FIG. 3, the conventional LED lamp unit 2 includes a red light emitting diode (R LED), a green light emitting diode (G LED), a blue light emitting diode (B LED) and a control circuit, as shown in FIG. 4. Two pins of the conventional LED lamp unit 2 are connected externally to the positive and negative terminals of the DC power, respectively. The control circuit can be realized as an integrated circuit (IC), which is used to drive the three primary colors RGB LED according to the procedure configured in the original circuit, or to conduct the mixing process of colors. However, the defect for the conventional LED lamp unit 2 is that they should be embedded with independent control ICs, so when applying in the lamp string, the color changing for each LED lamp unit 2 after power on is independently operated without synchronization. If each LED lamp unit 2 can be synchronized, the effect shown by the lamp string must be quite different from the star-studded effect by independent LED lamp units. Thus, how to take care the cost issue but with synchronous effect becomes the research direction in the industry.